Alcohol and other drug abuse is a pervasive problem among homeless, runaway youth. The purpose of this project is to investigate the prevalence, antecedents, and risk factors associated with alcohol and other drug abuse among homeless youth in the Hollywood area of Los Angeles, and use this information to develop and pilot an intervention for prevention. The project will be conducted by the Division of Adolescent Medicine at Childrens Hospital of Los Angeles. The specific aims of the project are to estimate the prevalence of alcohol and other drug use among homeless youth (Aim 1); identify antecedents and risk factors of homelessness, alcohol and other drug use, and HIV risk-related sexual behaviors among homeless youth (Aim 2); evaluate the degree to which sustained homelessness affects alcohol and other drug use patterns, and how alcohol and other drug use affects homelessness and impairs youths' physical health status (Aim 3); and document patterns of mobility and HIV risk-related behaviors among homeless youth in order to estimate their potential as vectors for HIV transmission in the general population (Aim 4). These aims will be accomplished by recruiting a sample consisting of 400 youth, ages 12 to 23 years, from a youth serving community-based agency (Los Angeles Youth Network) and administering an interview instrument. From this sample, we will invite 200 randomly selected respondents to participate in four follow-up interviews: at 30, 60, 90 and 180 days after the initial interview. The results from this epidemiologic research will then be used to develop and pilot a prototype intervention for the prevention of alcohol and other drug abuse as well as HIV risk-related sexual behaviors among homeless youth (Aim 5).